Powders are used in numerous applications. Powders are the building blocks of catalytic, electronic, telecommunication, electrical, magnetic, structural, optical, biomedical, chemical, thermal, and consumer goods. On-going market demands for more efficient, reliable, smaller, faster, superior, and more portable products have demanded miniaturization of numerous products. This, in turn, has demanded miniaturization of the building blocks, i.e. the powders. Nano-scale (or nanosize, ultra-fine) powders, with a size of 10 to 100 times smaller than conventional micron size powders, enable quality improvement and differentiation of product characteristics at scales currently unachievable by commercially available micron-sized powders.
Nano-scale powders, in particular, are a novel family of materials whose distinguishing features include a domain size so small that size confinement effects become a significant determinant of the materials' performance. Such confinement effects can, therefore, lead to a wide range of commercially important properties. Thus, nano-scale powders offer an extraordinary opportunity for design, development, and commercialization of a wide range of devices and products for various applications. Furthermore, since they represent a whole new family of material precursors where conventional coarse-grain physiochemical mechanisms are not applicable, these materials offer unique combination of properties that can enable novel and multifunctional components of unmatched performance. Other examples of sub-micron and nano-scale powder applications are described in U.S. Pat. No. 5,984,997, which is hereby incorporated by reference along with the references contained therein.
Traditional methods of producing fine metal powders chiefly involve plasma reactions, such as the process described in European Patent Application Publication EP 1619000169, which is hereby incorporated by reference, or the condensation from gas and liquid phase described in U.S. Patent Application Publication No. 20050277297, which is hereby incorporated by reference. These known methods require relatively high temperatures exceeding several hundred degrees Celsius so that metal grain sizes can rapidly grow during sintering. Moreover, these methods are inefficient and do not typically produce nano-scale powders. These methods consume a large amount of energy, and, therefore are expensive. Likewise, the production of metal powders from hydrogen reduced oxides is a well known technique; however, this process suffers from similar drawbacks. The great expense associated with traditional techniques of producing fine metal particles limits the applications in which the metal particles can be used.
U.S. Pat. No. 3,955,961 discloses processes for reducing certain metal carboxylates with hydrogen or carbon monoxide under low moisture conditions, relatively low temperatures and preferably high pressures. The patent teaches starting with relatively large (2.5 cm) pellets, increasing the hydrogen pressure to speed up the reaction rate and allowing the exothermic reaction to raise the temperature well above the beginning temperatures to thereby increase the production rate and decrease cost. The patent issued at a time (1976) long before the possible manufacture of submission or nano-particles was seriously contemplated.